This invention relates to a sheet handling device such as a sheet separating and feeding device, and more particularly to a sheet separating and feeding device suitable for use in an electrostatographic copying machine.
In the electrostatographic copying process, as originally disclosed in Carlson U.S. Pat. No. 2,297,691, a photoconductive insulating surface is electrostatically and uniformly charged, and exposed to a light pattern of the original to be reproduced to form a latent electrostatic image on the surface. The latent image is then developed by contacting the image areas with finely divided electrostatically attractive materials known as toner particles. The developed image is generally transferred to a final support material, such as a sheet of paper, and affixed thereto to form a permanent copy of the original.
Since the disclosure of this basic concept by Carlson, a variety of automatic copying machines and devices have been proposed and commercialized. Some of these machines and devices, including sheet feeding and transporting apparatus, are disclosed in the prior art. These prior art patents, as well as other patents relating to conveyor beltings, etc., will be now briefly described.
In Stange et al U.S. Pat. No. 3,469,834, there is disclosed a sheet feeder and separator apparatus in which a friction drive wheel engages the top sheet of a stack to advance the sheet between a stationary retard roll or abutment member and a moving belt member. The belt member is formed of a material having a high coefficient of friction, while a friction member is formed of a resilient material having a lower coefficient of friction and is mounted on the retard roll or abutment member and engageable with the belt member.
in Fackler U.S. Pat. No. 3,482,676, there is disclosed a document transport belt having an outer layer of a flexible light reflective material such as white rubber, and an inner layer of flexible electrically conductive material such as graphite impregnated rubber.
In Spear U.S. Pat. No. 3,645,615, there is disclosed a copying apparatus which is capable of being selectively operated to produce simplex image of an original document, or to produce duplexed image according to a second mode of operation in which the simplexed sheets are automatically delivered to a second supply tray for refeeding through the copying processing stations. In the duplex mode of operation, simplexed sheets are forwarded to an upper supply tray shown in FIG. 3 of this patent. The driven feed rollers in this upper supply tray are then in contact with the imaged side of the simplexed sheet when feeding the simplexed sheet through the copying apparatus for the duplexed image on the reverse side of the sheet.
In Anderson et al U.S. Pat. No. 3,738,859, there is disclosed a fire resistent conveyor beltings for underground mining operations, which is made of a texitle carcass impregnated with polyvinyl chloride (PVC), an inner layer of PVC or other thermoplastic material, and an outer layer of natural or synthetic rubber such as butadiene-acrylonitrile copolymer rubber. The rubber compound is so formulated that under frictional heat, a differential softening occurs at the PVC/textile interface causing the rubber layers to be detached.
In Stange U.S. Pat. No. 3,768,803, there is disclosed a sheet feeder made of a feeder belt in contact with a stack of sheets and a retard member. The feed belt has a layer of natural rubber on top, a rayon cord layer, and a tracking member made of an elastic material such as neoprene. The retard member has a pad thereon made of a resilient material. The feeder belt and retard member together form a throat in which the sheets are separated.
In Amatangelo U.S. Pat. No. 3,931,090, there is disclosed a highly reversion resistant polyisoprene elastomer composition vulcanized with a low sulphur content for use in paper feed belts The low sulphur vulcanizate of isoprene provides high resistant to physical degradation due to dynamic mechanical stress under operating conditions.
In Taylor et al U.S. Pat. No. 3,949,979, there is disclosed a sheet feeding apparatus having a belt and retard pad, with the retard pad pivoted about a pin so that the nip force is reduced when one attempts to remove a sheet in the reverse direction but the nip force is increased when the apparatus is feeding sheets in the feeding direction.
In Prince et al U.S. Pat. No. 4,019,941, there is disclosed a method of constructing conveyor belting by placing steel reinforcing cords in groves formed between the mating faces of layers of PVC based material.
Finally, in Perun et al U.S. Pat. No. 4,192,497, there is disclosed a composition for the surface of sheet separating devices, which comprises microcellular elastomeric material having a hardness of at least 25 durometer. Examples of microcellular elastomers include PVC, polyurethanes, styrene/acrylonitrile, and polyethylene. Certain disadvantages of silicone rubber retard roll and conventional polyurethane are briefly discussed (column 6, lines 5-16).
Although the sheet separating and feeding devices of the prior art have provided satisfactory services, there is a need for improved sheet feeding devices for use in electrostatographic copying machines. In particular, there is a need for improved sheet feeding devices which have stable and high coefficients of friction for dependable separation and feeding of sheets of paper; high resistance to air oxidation and ozone attack; and improved frictional properties when used in the duplex mode and in contact with sheets of paper having toner particles and silicone oil thereon; etc. As used herein , the terms "sheet feeding device" and "sheet separating and feeding device" are intended to refer to the same thing: that is, a device that will first separate a sheet from a stack and then feed that separated sheet to further processing stations. See, e.g., said U.S. Pat. No. 3,768,803 and FIG. 1 herein below.
It is, therefore, an object of the present invention to provide an improved sheet feeding device or sheet handling device for use in electrostatographic copying machines.
It is another object of the present invention to provide an improved sheet feeding device in which at least the functional surface of a feeding member has improved frictional stability.
These and other object of the invention will be apparent from the following disclosure.